It is the purpose of this project to develop methods for altering the antigenicity of nonimmunogenic tumors and to analyze the cellular and molecular basis of tumor rejection. The current areas of interest are: a) the induction of transplantation antigens by in vitro treatment of tumor cells with mutagen; b) the basis of recurrence of retrovirus-infected fibrosarcoma cells; and c) the role of Ia antigens in the rejection of a B cell leukemia.